Process and device for simulated moving bed separation with a reduced number of valves

Abstract

A simulated moving bed (SMB) separation device comprising a column, beds Ai of adsorbent separated by plates Pi with a single distribution and extraction network for fluids, in particular feed F, desorbant D, raffinate R and extract B, and a plurality of two-way valves for distribution of said fluids, said valves being limited in number compared with the prior art. The column is divided into a plurality of sectors Sk with 2 or 3 superimposed plates, each sector Sk comprising an external bypass line Lk connected to each plate Pi of Sk via a connector comprising a plate valve Vi. Each line Lk comprises a controlled means for limiting its internal flow, and is connected to each of the fluid networks F, D, R, E via a single line comprising a single controlled two-way isolation valve to supply for sequential supply or withdrawal of the corresponding fluid F, D, R or E towards or from the sector Sk under consideration. The SMB device may be used for the separation of para-xylene or meta-xylene from an aromatic C8 cut.

1. A device for separating at least one desired compound from a mixture comprising said compound, by simulated moving bed adsorption comprising:
 at least one column divided into a plurality of adsorbant beds Ai separated by distributor/extractor plates Pi for sequential supply and extraction of at least two supply fluids: a feed F and a desorbant D, and at least two withdrawn fluids: a raffinate R and an extract E, Pi being disposed between the bed Ai and the immediately inferior bed Ai+1; the device also comprising networks of fluids, i.e. at least a feed network P-net, a desorbant network D-net, a raffinate network R-net and an extract network B-net, each of said networks being connected to the column via a plurality of lines comprising two-way controlled isolation valves termed network valves, for sequential supply or withdrawal of said fluids; 
 in which the column is divided, over at least the major portion of its height, into a plurality of superimposed adjacent sectors Sk, each sector sk essentially being constituted by a group of at least 2 and at most 5 successive beds of adsorbant and by distributor/extractor plates Pi which are disposed immediately below said successive beds of adsorbant; 
 each of the distributor/extractor plates Pi of each of the sectors Sk is a single common network for sequential supply and withdrawal of fluids F, D, R, E; 
 the plates Pi of each sector Sk are connected together via an external bypass line Lk connected to each plate Pi of Sk via a connector comprising a single two-way controlled isolation valve belonging to the plate Pi, termed the plate valve Vi, for sequential supply or withdrawal of fluids F, D, R, E into or from Pi; 
 each of said bypass lines Sk comprises at least one controlled means for limiting the flow rate in Lk, which is either installed on the line Lk or in a bypass around a plate valve Vi of a plate Pi of Sk; 
 in which the bypass line Lk of each of the sectors Sk is connected to each of the networks F-net, D-net, R-net and E-net via a single line comprising a single network valve, respectively V Fk , V Dk , V Rk , V Ek , for sequential supply or withdrawal of the corresponding fluid F, D, R, E to or from the sector Sk under consideration; and in which each plate Pi of the sector Sk is uniquely connected to each of the networks F-net, D-net, R-net and B-net via, in series, the connector comprising the plate valve Vi then at least a portion of Lk then said single line comprising said single network valve, respectively V Pk , V Dk , V Rk , V Ek . 
 
   
   
     2. A device according to  claim 1 , in which each sector Sk is essentially constituted by a group of 2 or 3 successive beds of adsorbant. 
   
   
     3. A device according to  claim 1 , in which the bypass line Lk has an internal diameter equal to at least the largest opening diameter of the network valves connected to Lk. 
   
   
     4. A device according to  claim 1 , in which at least one sector Sk is constituted by two beds of adsorbant Aj, Aj+1 and the two distributor/extractor plates Pj, Pj+1 which are respectively disposed immediately below the beds of adsorbant. 
   
   
     5. A device according to  claim 4 , in which all of the sectors Sk are constituted by two beds of adsorbant and the two distributor/extractor plates which are respectively disposed immediately below the beds of adsorbant or said assimilated lower outlet line. 
   
   
     6. A device according to  claim 4 , in which at least one sector Sk is constituted by three beds of adsorbant Aj, Aj+1, Aj+2 and the three distributor/extractor plates Pj, Pj+1, Pj+2 which are respectively disposed immediately below said beds of adsorbant. 
   
   
     7. A device according to  claim 1 , in which at least one sector Sk is constituted by three beds of adsorbant Aj, Aj+1, Aj+2 and the three distributor/extractor plates Pj, Pj+1, Pj+2 which are respectively disposed immediately below said beds of adsorbant. 
   
   
     8. A device according to  claim 7  in which, for each sector Sk with three plates Pj, Pj+1, Pj+2, the bypass line Lk comprises a first means for limiting the flow between Pj and Pj+1 and a second means for limiting the flow between Pj+1 and Pj+2. 
   
   
     9. A device according to  claim 1 , in which the whole column is constituted by said adjacent superimposed sectors Sk, the column comprising a lower outlet line assimilated to a plate Pn corresponding to the lower bed of adsorbant An. 
   
   
     10. A device according to  claim 1 , in which each of said bypass lines Lk comprises at least one controlled means for limiting the flow circulating in Lk, which is installed as a bypass about a plate valve Vi of a plate Pi of Sk. 
   
   
     11. A device according to  claim 10 , in which said means for limiting the flow circulating in Lk installed as a bypass around said plate valve Vi comprises a controlled valve with a smaller diameter opening than that of Vi.